1. Field of the Invention
The present invention relates to an apparatus to be used for demonstration of various phenomena associated with the movement of the earth about the sun and about its own axis, such as day and night, the changes in their relative length, the seasons, the equinoxes and solstices, and the constancy of the orientation of the earth's axis of rotation relative to a fixed point in space.
2. Brief Description of the Related Art
Such apparatuses are known and available under the name of "Tellurion," and can indeed be used to demonstrate the above phenomena. These table-top devices, operable either manually by means of a crank, or electrically, consist of a heavy stand, a horizontal arm mounted on, and rotatable about, this stand, a light source representing the sun, mounted on, and rotating with, this arm and a rotatable globe with its axis at an angle with the vertical of about 23.5.degree., mounted on a small pedal which is itself rotatably mounted on the free end of the arm. While it is relatively simple to convert the cranking of a handle or the output of an electric gear motor into a revolving movement of the arm, causing the globe to "orbit" the "sun" and, by means of another set of gears, make the globe rotate about its axis during this orbital movement, a serious complication of the entire system is due to the fact that, in order to preserve the above-mentioned constancy of orientation of the globe's axis, the pedestal has to be imparted a compensatory movement equal in speed, but opposite in sense, to the movement of the arm. This requires the provision of a sophisticated, epicyclic, multicomponent gear system that is very expensive, especially if produced to industrial standards to ensure trouble-free operation and a reasonably long service life even, and especially, under conditions of rough treatment and lack of proper maintenance, as is to be expected, e.g. in schools.